System for separation of oxygen from air



y 1950 P. E. HAYNES 2,514,391

svs'rm FOR SEPARATION OF OXYGEN mou AIR Filed Jan. 29, 1948 IN V f N TOR: P154225 E HA Y/wss.

G Qdav ins Patented July 11, 1950 SYSTEM FOR SEPARATION OF OXYGEN FROM AIR Pierre E. Haynes, Indianapolis, Ind., asslgnor to Koppel-s Company, Inc., a corporation of Delaware Application January 29, 1948, Serial No. 5,017

4 Claims. 1

The present invention relates to improvements in systems for the separation of oxygen from air. More particularly, the invention relates to improvements in the well-known Linde-Friinkl procedure and apparatus, and methods of operating such or other apparatus in which cold accumulators are employed for separating oxygen of high purity from air.

There is at present a considerable demand for oxygen of above 99% or 99.5% to 100% purity, as in cutting of steel with oxyacetylene flame. The oxygen supplied for this purpose must be of said high purity in order to function properly in present day steel plant equipment. In the normal operation of Linde-Frankl units for instance, oxygen of only 90% to 95% purity is produced. At best, such units have produced oxygen of not greater than 98% purity.

An object of the present invention is to provide improvements whereby oxygen of 99% or 99.5% purity or better is obtained efficiently and economically on a large scale by use of the Linde- Friinkl air-separation system or systems of this type with which cold accumulators are associated. Another object lies in providing for the correction of imbalance in Frankl accumulators of such systems wherein the quantity of cold gases caused to leave the accumulators is or becomes less than the quantity entering the same for their subsequent fractionation. A further object is to provide improvements whereby the purity of oxygen is kept uniformly high during its production in the above air-separation processes.

In the Linde-Frankl process for producing a nitrogen fraction and an oxygen fraction, air is compressed in a turbine compressor and cooled in two pairs of accumulators, one pair of which is fed with a previously separated nitrogen fraction and the other pair with a previously separated oxygen fraction. The incoming air thus cooled is separated in a double column of the ordinary Linde type. In the present invention, during the operation of a Linde-Friinkl air separation process, for instance, a small proportion oithe separated oxygen is diverted from the stream passing to the oxygen accumulators and is subjected to certain liquefaction and rectification treatments whereby oxygen of 99% or 99.5% purity or higher is obtained, while provision is made for compensating for imbalance in the accumulators.

By way of illustration, one method and means of carrying out the invention will be described hereinbelow with reference to the accompanying diagrammatic drawing.

compressor I for incoming air is connected by a pipe 2 to the warm ends of two pairs, 3 and 4, of cold accumulators. The air from the cold ends of the accumulators is fed through a pipe I to be separated in the usual manner as in a double rectifying column 6 of the Linde type. Separated oxygen passes from the column 6 to the accumulators 3, and the separated nitrogen passes from this column to the accumulators 4, through pipes 'l and 8 respectively. The oxygen, usually drawn off through pipe 9, varies in purity between to To obtain oxygen of increased purity (above 99%) by means of the present invention. cold 90%-95% oxygen at its saturation temperature is withdrawn at l0, adjacent the cold ends of the accumulators 3, and is passed through a pipe ll of a heat exchanger I2; compressed to about 5 to 10 atmospheres absolute in a compressor i3; passed at this pressure back through the heat exchanger H by means of a pipe ll to which is transferred the cold from the gas in pipe ll before compression; and thence through a pipe II to a reboiler coil 16 in a kettle I! at the base of a column ii. The 90-95% 02 liquefied in the coil I6 is delivered through a pipe 19 to a valve 20 through which it is expanded to about 1.5 atmospheres absolute into the top of the column II. In this column, which has about ten to twelve plates, the oxygen is rectified to a liqui de'containing 99.5-100% oxygen in the kettle ll, and a gas mixture at the top of the column rich enough in oxygen to warrant its addition to the 90-95% oxygen product in pipe 9. Before such addition, the said gas mixture is passed through a pipe 2|, pipe 22 of the heat exchanger 12, and pipe 28 connected to the pipe 9.

The 99.5-100% oxygen in the kettle I1 is withdrawn through a pipe 24 and valve 25, and delivered to the heat exchanger I! in contact with the pipes/l I, I4 and 22 therein. This oxygen of high purity is obtained as a product through a pipe 18.

During the operation of the apparatus shown and in the manner described. in order to comat point 10 of the Linde-Friinkl system, a quantity of air is added by means of an auxiliary compressor 21 suflicient to compensate for the withdrawn oxygen. Thus if 10% of the oxygen product at point It is withdrawn for rectification, an equivalent quantity of additional air is introduced In the drawing. apparatus is shown in which a so at the compressor 21. If desired, this oxygen withdrawal and air introduction may be automatically controlled.

The above-mentioned additional air introduced at the compressor 21 is preferably over and above the volumetric addition of air made in the ordinary operation of the Linde-Frlinkl system, and made ordinarily to correct for thermal imbalance of the accumulators and to allow added volume of N: plus 02 backward through the accumulators and to effect more perfect evaporation of impurities frozen out from the warm air entering in the opposite direction.

Air from the compressor 21 is cooled with emmonia in a heat exchanger 28 primarly to dehydrate the air. This air is passed through a pipe 29 successively through heat exchangers 30 and 3| ordinarily provided in the Linde-Frankl system; and then through a coil 32 in the kettle IT to supply the extra heat required to evaporate nitrogen and a. portion of the oxygen therein. From the coil 32, the air is expanded through a valve 33 and introduced into the upper column of the Linda double column 6 at a level preferably between that of the usual sprays 34 and 35, respectively for the nitrogen and low pressure air from the lower column.

The invention hereinabove set forth is embodied in particular form and manner but may be variously embodied within the scope of the claims hereinafter made.

I claim:

1. A process of separating oxygen of high purity from air, which process comprises refrigerating air at elevated pressure in cold accumulators cooled to relatively low temperature, rectifying the refrigerated air into its major constituents including an oxygen fraction and a nitrogen fraction, separately withdrawing said fractions and cooling said accumulators therewith while diverting a portion of said oxygen fraction passing to said accumulators, liquefying said portion of said oxygen fraction and rectifying said portion to a mixture containing above 99% oxygen while adding air in the first-mentioned, rectification to correct for imbalance in the accumulators and in a quantity equivalent to the quantity of the said diverted portion of said oxygen fraction, and withdrawing the oxygen of above 99% purity.

2. A process of separating oxygen of high purity from air, which process comprises refrigerating air at elevated pressure in cold accumulators cooled to relatively low temperature, rectifying the refrigerated air to a nitrogen fraction and to a fraction containing about 90 to 95% oxygen, separately withdrawing said fractions and cooling said accumulators therewith while diverting a portion of said oxygen fraction passing to said accumulators, compressing the said portion to a pressure of about 5 to 10 atmospheres, liqucfying the said portion, and rectifying said portion to a mixture containing above 99% oxygen while adding air in the first-mentioned rectification in a quantity sufficient to compensate for imbalance in the accumulators and equivalent to the quantity of the said diverted portion of said oxygen fraction, and withdrawing the oxygen of above 99% purity.

3. A process in accordance with claim 1 in which the imbalance in the accumulators is corrected by' compressing an amount of air equivalent to thmamount of said portion of said oxygen fraction, cooling the said latter air in heat-exchange relationship with cold separated nitrogen in said first-mentioned rectification, passing said latter cooled air into heat exchange relationship with liquid oxygen of above 99% purity obtained in the second mentioned rectification and introducing the so treated latter air in the first-mentioned rectification for fractionation with the first-mentioned air.

4. Apparatus for separating oxygen of high purity from air, comprising a plurality of cold accumulators, a, z-stage rectification means, means for forcing air through said accumulators and into said rectification means, means for conducting an oxygen fraction and a nitrogen fraction separately from said rectification means to said accumulators, means for diverting a portion of said oxygen fraction before reaching the accumulators and for conducting same under pressure in heat-exchange relationship with said diverted portion, a fractionation column for said portion, a coil in the bottom of said column, means for conducting said compressed, cooled portion to said coil, means for introducing said portion from said coil into the top of said column, means for conducting under pressure in heat-exchange relationship with a nitrogen fraction from the first of said 2-stage rectification means and in heat-exchange relationship with liquid in the bottom of said fractionation column an amount of air equivalent to the amount of said diverted portion of said oxygen fraction, and means for introducing said last-named air into the second of said Z-stage rectification means.

PIERRE E. HAYNES.

Name Date Frankl May 28, 1935 Number 

1. A PROCESS OF SEPARATING OXYGEN OF HIGH PURITY FROM AIR, WHICH PROCESS COMPRISES REFRIGERATING AIR AT ELEVATED PRESSURE IN COLD ACCUMULATORS COOLED TO RELATIVELY LOW TEMPERATURE, RECTIFYING THE REFRIGERATED AIR INTO ITS MAJOR CONSTITUENTS INCLUDING AN OXYGEN FRACTION SAND A NITROGEN FRACTION, SEPARATELY WITHDRAWING SAID FRACTIONS AND COOLING SAID ACCUMULATORS THEREWITH WHILE DIVERTING A PORTION OF SAID OXYGEN FRACTION PASSING TO SAID ACCUMULATORS, LIQUEFYING SAID PORTION OF SAID OXYGEN FRACTION AND RECTIFYING SAID PORTION TO A MIXTURE CONTAINING ABOVE 99% OXYGEN WHILE ADDING AIR IN THE FIRST-MENTIONED RECTIFICATION TO CORRECT FOR IMBALANCE IN THE ACCUMULATORS AND IN A QUANTITY EQUIVALENT TO THE QUANTITY OF THE SAID DIVERTED PORTION OF SAID OXYGEN FRACTION AND WITHDRAWING THE OXYGEN OF ABOVE 99% PURITY. 